It was previously proposed to detect the lateral acceleration or the yaw rate of a vehicle, and improve the dynamic property of the vehicle by steering the rear wheels appropriately (refer to Japanese patent laid open publication No. 57-44568).
According to this prior patent publication, the system is not able to distinguish between the yaw rate produced by the turning maneuver of the vehicle and the yaw rate produced by such external disturbances as side wind, and, therefore, it was not possible to achieve both a satisfactory immunity against external disturbances and a favorable maneuverability because the rear wheels are steered according to the yaw rate produced without regard to the cause of the yaw rate.
It is conceivable to change the yaw rate gain according to the vehicle speed so that a desired maneuverability may be obtained in a low speed range and a sufficient immunity against external disturbances may be obtained in a high speed range. However, such a speed dependent change in the vehicle response tends to cause some discomfort to the vehicle operator.